Internal combustion engines are often cooled by circulating a liquid, typically water mixed with coolant, through the engine block. The liquid circulates in small passages, undergoing heat exchange with the hot engine. The heated liquid then passes through a radiator, which transfers heat from the liquid inside the radiator pipes to air outside the radiator, thereby cooling the liquid. The liquid is then re-circulated to the engine. A water pump assists in circulating the liquid, and a fan assists the radiator's heat exchange by blowing air upon the radiator's surfaces.
In automotive vehicles, the above-described engine radiator is typically mounted in a position where it receives airflow from the forward movement of the vehicle, such as behind a front grill. This engine radiator is sometimes referred to as the “main” radiator because the vehicle's cooling system may also include additional, usually smaller, radiators.
For example, additional radiators are sometimes used to cool automatic transmission fluids, air conditioner refrigerant, intake air, motor oil or power steering fluid. For cooling motor oil, a small radiator used to cool the engine oil is referred to as an “oil cooler”.
For engines equipped with exhaust gas recirculation (EGR), another type of cooler that may be part of the vehicle's cooling system is an EGR cooler. An EGR cooler reduces exhaust gas temperatures prior to recirculating the exhaust back to the engine's intake system. Typically, the EGR cooler uses liquid coolant and is in fluid communication with the rest of the vehicle's overall cooling system.